NO. 2 DIMENSIONS OF FLYING ANIMALS — GREENEWALT 7 



an average of 17 percent for ordinary birds. Hence one would expect 

 hummingbirds to be relatively more powerful fliers. The ratio of the 

 weights of the two muscles for hummingbirds is roughly 2 as compared 

 with 10 for ordinary birds. One can then safely assume that both up- 

 beat and downbeat contribute power for flight. This is also what one 

 would expect from the pattern of the wing beat seen in high-speed 

 moving pictures. 



In figure 17, total muscle weight is plotted against body weight for 

 insects. We see the usual scatter typical of dimensional data for insects. 

 However, for many insects, notably the Neuroptera, Diptera, and 

 Hymenoptera, total muscle weight is roughly the same percentage of 

 body weight as is found for birds. For the butterflies, however, the 

 musculature is very light, correlating with their poor flight perform- 

 ance. 



Admittedly these same data could have been presented in many dif- 

 ferent ways. No attempt has been made, aside from figure 4, to sub- 

 divide the insects and birds into families and genera. Such an effort 

 might well be fruitful, but the data collected here are probably not 

 sufficiently precise to permit more than the broadest generalization. It 

 is possible that relationships such as these will be of significance in 

 taxonomic investigations both for insects and birds. It is to be hoped 

 that someone will find the rather tedious investigations worth the effort. 



